PHOENIX -- General manager Kevin Colbert admitted there is some unknown when it comes to the Pittsburgh Steelers' only free-agent signing as far as outside players.

And it has little or nothing to do with running back DeAngelo Williams (pictured) residing on the wrong side of 30 or the fact that he will be entering his 10th NFL season in 2015.

The question with Williams is how he will adjust to backing up Le'Veon Bell, a role that could come with fluctuating playing time and limited touches.

The Steelers tried to pair a veteran back last season with Bell and it failed miserably as LeGarrette Blount pouted his way out of Pittsburgh after his role in the offense diminished.

The Steelers have essentially hit a reset with the signing of Williams, and Colbert said there is one major difference compared to when they signed Blount.

"After his rookie year I think you could say (Bell) was a good back," Colbert said. "After last year I think everybody can agree he’s a very good back. I think someone coming in has a better understanding of who (Bell) is, or they should."

Colbert said the Steelers won’t know how Williams deals with a limited role until he is dealing with the reality of it.

But the Carolina Panthers' all-time leading rusher received a strong endorsement from quarterbacks coach Randy Fichtner, who recruited Williams to Memphis and coached him there. And Williams said all of the right things while the Steelers were courting him.

"Meeting him and hearing Randy talk about his character and his willingness to be a contributor really sealed the deal for us," Colbert said. "And then to bring him in, visit with him and have him say the things that he said about trying to win a championship, that was important. We’ll see how it goes."

Williams, who turns 32 next month, will likely start the first two games of the season with Bell facing a suspension for violating the personal conduct policy. Colbert said the Steelers see Williams as more than just injury insurance at running back after Bell serves his suspension.

"The starting running back, I don’t care how good they are it’s a little hard to play every down as the starter in this league at that position," Colbert said. "So you want to have someone that’s been there, done that, but is still not worn out either. You still want some life and you want him to accept the role that we presented. I think that anybody coming in it’s a different scenario than it was last year."